Basically, the distance measurement equipments in present can be categorized to two types, one is the contact distance measurement equipment and the other is the contactless distance measurement equipment. The contact distance measurement equipment, such as the coordinate measurement machine (CMM) which is often realized by the traditional distance measurement method, has an advantage of having a higher accuracy; however, the object may be damaged by the contact distance measurement equipment while the object is physically contacted to the contact distance measurement equipment. Therefore, it is not proper to adopt the contact distance measurement equipment to measure the position of a high-value object.
Compared to the contact distance measurement equipment, the contactless distance measurement equipment has a much higher operation frequency which is over millions per second, so as the contactless distance measurement equipment has a wider application field. The contactless distance measurement equipments can be further categorized to two types, one is the active-and-contactless distance measurement equipment and the other is the passive-and-contactless distance measurement equipment. In the active-and-contactless distance measurement equipment, a power wave is first projected to an object, and the position of the object is then determined through computing the distance between the object and a reference position; wherein the power wave can be a visible light, a high energy light beam, an ultrasonic wave, or a X-ray.